Applicant's Abstract The broad aim of this research program is to gain insights into the regulatory mechanisms that control the growth and development of cardiac muscle. This proposal examines the role of epigenetic mechanisms in the etiology of diabetic cardiomyopathy. Previous work with a transgenic animal model of cardiac failure and analyses of both animal and human failing hearts suggests that de novo DNA methylation plays an important role in modulating the pattern of gene expression in the heart. In the transgenic model, the methylation of specific gene sequences is sufficient to produce the structural and functional changes of the heart associated with moderate heart failure. These effects of DNA methylation are intrinsic to the heart since the altered heart function in the transgenic model occurs in the absence of cardiovascular disease, hypertension, or any overt developmental defects. In animal and human failing hearts, selective methylation of the same gene sequences is correlated with hypertrophy and congestive heart failure. Preliminary data indicate that similar changes in DNA methylation are found in human diabetic cardiomyopathy. It is postulated that specific gene sequences are methylated de novo in diabetes and that these changes in DNA methylation mediate the structural and functional alterations found in diabetic hearts. To examine this hypothesis, the methylation of specific regions of the genome will be assessed in human hearts diagnosed with diabetic cardiomyopathy. This analysis will reveal if selective sequences are differentially methylated, if the pattern of de novo methylation differs from that observed in failing hearts due to idiopathic cardiomyopathy or coronary artery disease, and if these alterations in methylation reflect more global changes in DNA methylation. To determine whether diabetes itself induces de novo DNA methylation, the temporal changes in DNA methylation following the onset of diabetes will be assessed in an animal model. Finally, the role of specific DNA methylation sites in modulating the heart phenotype will be assessed by a mutational analysis in a transgenic mouse model. Defining a role for DNA methylation in diabetic cardiomyopathy may not only identify a new gene regulatory mechanism for the cardiac effects of diabetes but also would provide more insight into novel epigenetic mechanisms that can reprogram gene expression and the phenotype of the heart.